DIAGNOSIS Most likely a failed internal fuse on the main control board or a disconnected power cable inside.
FIX Unplug it. Remove the rear grill (several screws). Locate the small glass fuse on the control board near where the power cord attaches. Test it with a multimeter for continuity. If blown, replace it with an identical 250V 2A slow-blow fuse.
IF THAT DIDN'T WORK The power supply module on the control board may have failed. This requires a board replacement. The part number is typically stamped on the board.
HEADS UP Capacitors on the board can hold a charge even when unplugged. Do not touch the board with metal tools unless you know how to safely discharge them.